The present invention relates to ceramics used for making various electronic components and a method for manufacturing ceramics.
Conventional ceramics are manufactured by mixing an organic binder with a powder of conventional ceramics material, pressing the mixture into a mold, and then sintering the mold at a high temperature. However, conventional ceramics manufactured by conventional methods are susceptible to relatively large volumetric shrinkage during the high temperature sintering step, thereby making it very difficult to obtain ceramics having precise and accurate dimensions. As a result, conventional sintered ceramics must undergo time-consuming cutting or grinding steps to obtain a particular shape and dimension. However, because of the high hardness of sintered ceramics, such cutting or grinding steps involve expensive machining costs.
Japanese Laid-Open Patent, Hei 1-317157 discloses ceramics having a precise shape and dimension. The disclosed ceramics are produced without the problem of volumetric shrinkage, thereby obviating the need for grinding or cutting. The disclosed ceramics are manufactured using a so-called reactive sintering method wherein alumina powder, which possesses dual functions of high electrical insulation and thermal conductivity, is mixed with titanium powder. The mixture is press-molded into a metal die and then sintered in a nitrogen atmosphere. The structure of the disclosed ceramics is characterized by a reactively sintered body, in which the alumina powder is reactively combined with the titanium nitride powder that is derived from the metal titanium powder during the sintering step. Volumetric shrinkage during the sintering step is minimized because the metal titanium powder reacts with nitrogen gas and expands. Thus, an alumina-system ceramics of low dielectric constant can be obtained when it is combined with titanium nitride, which is a material of low dielectric constant.
During the disclosed manufacturing process, however, nitrogen gas reacting with the metal powder must be externally supplied into the mold via pores located in the mold. As a result, the disclosed reactively-sintered ceramics inherently exhibit low mechanical strength or considerably lessened inorganic functional material characteristics caused by the numerous pores that are produced within the ceramics at a volume ratio of as high as 15 to 20%. Further, sintering within a nitrogen atmosphere requires strict regulation of the nitrogen density and the sintering temperature, which is disadvantageous from the stand point of manufacturing cost.
It is well known that the highest function of ceramics can be obtained when the porosity of sintered ceramics is at a minimum. Further, ceramics having a high thermal conductivity can be obtained when the ceramics is only made of alumina. Ceramics having a highest magnetic saturation can be obtained when the ceramics is made of magnetic material only. Ceramics having a high dielectric constant can be obtained when it is made of a dielectric material only. In addition, ceramics having high thermal conductivity can be obtained using conventional manufacturing methods wherein metal particles are transformed into metal nitride particles by the disadvantageously expensive reactive-sintering method in a nitrogen atmosphere.